首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6565篇
  免费   86篇
  国内免费   15篇
电工技术   38篇
综合类   15篇
化学工业   456篇
金属工艺   54篇
机械仪表   54篇
建筑科学   116篇
矿业工程   34篇
能源动力   114篇
轻工业   354篇
水利工程   22篇
石油天然气   14篇
武器工业   1篇
无线电   269篇
一般工业技术   366篇
冶金工业   4413篇
原子能技术   31篇
自动化技术   315篇
  2022年   23篇
  2021年   50篇
  2020年   22篇
  2019年   31篇
  2018年   42篇
  2017年   29篇
  2016年   45篇
  2015年   50篇
  2014年   78篇
  2013年   136篇
  2012年   106篇
  2011年   130篇
  2010年   96篇
  2009年   100篇
  2008年   136篇
  2007年   120篇
  2006年   96篇
  2005年   106篇
  2004年   77篇
  2003年   76篇
  2002年   64篇
  2001年   74篇
  2000年   44篇
  1999年   168篇
  1998年   1422篇
  1997年   841篇
  1996年   501篇
  1995年   314篇
  1994年   241篇
  1993年   272篇
  1992年   78篇
  1991年   56篇
  1990年   74篇
  1989年   67篇
  1988年   70篇
  1987年   58篇
  1986年   63篇
  1985年   59篇
  1984年   21篇
  1983年   30篇
  1982年   29篇
  1981年   32篇
  1980年   44篇
  1978年   29篇
  1977年   103篇
  1976年   204篇
  1975年   23篇
  1973年   17篇
  1972年   12篇
  1969年   12篇
排序方式: 共有6666条查询结果,搜索用时 15 毫秒
931.
Cytotoxic T lymphocytes provide protection against persistent infection of the central nervous system by the JHM strain of mouse hepatitis virus. In BALB/c (H-2d) mice, the dominant response is directed against an Ld-restricted peptide in the nucleocapsid protein (APTAGAFFF). Characterization of the fine specificity of this response revealed that the predicted anchor residues at positions 2 and 9 were the most critical for class I binding. Amino acids at positions 7 and 8 were identified as T-cell receptor contact residues. Virus-induced cytotoxic T lymphocytes to other Ld motif-containing nucleocapsid peptides were not detected, despite the identification of two epitopes with reduced Ld affinity. These data suggest that mutations within four residues of the dominant epitope could contribute to the persistence of the JHM strain of mouse hepatitis virus.  相似文献   
932.
933.
The integral equation for cylindrical Poiseuille flow of a general excitation gas is derived for diffuse scattering at the wall. For a degenerate Fermi gas or liquid the flow through a circular cylindrical tube is determined numerically by a variational method.  相似文献   
934.
935.
The aim of this study was to investigate the long term effect of 131I treatment on thyroid function and size in patients with non-toxic multinodular goitre. The subjects were 69 consecutive patients with multinodular non-toxic goitre selected for 131I treatment and followed for a minimum of 12 months. Outcome measures were standard thyroid function variables and ultrasonically determined thyroid volume before and after treatment. Fifty-nine patients were treated with a single dose of 131I, 12 with two doses, and one with four doses. In 45 patients treated with one dose who remained euthyroid the median thyroid volume was reduced from 73 (interquartile range 50-106) ml to 29 (interquartile range 23-48) ml at 24 months. The median reduction was 40 (22-48) ml, half of which occurred within three months. Patients treated with two doses as well as those developing hypo- or hyper-thyroidism also had a significant reduction in thyroid volume. Eleven patients developed hypothyroidism (cumulative five year risk 22%). Side effects were few. In conclusion we find that 131I treatment of multinodular non-toxic goitre is an attractive alternative to surgery.  相似文献   
936.
Hyperpolymorphism of minisatellite DNA, detected using the M13 bacteriophage DNA hybridization probe, was studied in three ethnographic groups of Bashkirs and in the Komi population. Bands from 2 to 20 kb were analyzed in hybridization patterns. A significant population difference was detected both in evaluation of the average number of hybridization fragments per individuals and in the distribution of frequency of some fractions. Thus, it seems possible to describe a set of so-called characteristic fractions for each population. According to the hybridization fragment frequency for the populations investigated, an index of genetic similarity was calculated. The possibility of using this kind of multiple polymorphism of DNA in population genetic investigations at the level of ethnic groups and peoples is discussed, and a conclusion is made about the necessity of searching for the most informative methods of analyzing the data obtained.  相似文献   
937.
This prospective cohort study was designed to test whether a distinct fatigue syndrome existed after the onset of glandular fever. Two hundred and fifty primary care patients, with either glandular fever or an ordinary upper respiratory tract infection (URTI) were interviewed three times in the 6 months after the clinical onset of their infection. At each interview a standardized psychiatric interview was given and physical symptoms were assessed. There were 108 subjects with and Epstein-Barr virus (EBV) infection; 83 subjects had glandular fever not caused by EBV and 54 subjects had an ordinary URTI. Five subjects were excluded because they had no evidence of an infection. Principal components analyses of symptoms supported the existence of a fatigue syndrome, particularly in the two glandular fever groups. The addition of symptoms not elicited by the standard interviews gave the full syndrome. This included physical and mental fatigue, excessive sleep, psychomotor retardation, poor concentration, anhedonia, irritability, social withdrawal, emotional lability, and transient sore throat and neck gland swelling with pain. A fatigue syndrome probably exists after glandular fever.  相似文献   
938.
Pseudomonas species S-27 was grown on various substrates. It was established that the Pseudomonas species S-27 strain can produce biosurfactants of ramnolipid nature decreasing the surface and interfacial tension to 29.2 and 0.05 mN/m. respectively, as well as a biopolymer stabilizing the emulsions with hydrocarbons and oils. The biosurfactant and bioemulsifier synthesis is shown to depend of the substrate nature.  相似文献   
939.
To determine the influence of adjuvant on the induction of antibodies to thyrotropin receptor (TSHR), we immunized BALB/c mice with a extracellular domain of the TSHR (ETSHR) protein in complete Freund's adjuvant (CFA), Titer Max (TM) and Gerbu. Similarly, control groups of mice were immunized with bovine serum albumin (BSA) in each of the different adjuvants. As determined by ELISA, ETSHR given along with CFA elicited high titers of antibodies to ETSHR which were mainly restricted to the IgG1 subclass. Mice immunized with ETSHR in TM also developed high titers of anti-ETSHR antibodies but had higher levels of both IgG1 and IgG2a. However, immunization with ETSHR in Gerbu resulted in low titers of antibodies, restricted to IgG1 subclass. Immunization of mice with BSA in each of the three adjuvants induced higher antibody titers to BSA. The subclass of antibodies in mice immunized with BSA in CFA and TM were predominantly IgG1 and IgG2a with lower levels of IgG2b, whereas in Gerbu treated group, antibody to BSA was restricted to IgG1 subclass. Analysis of specificity of antibodies against ETSHR, in mice immunized with ETSHR, revealed that irrespective of the adjuvant used, the dominant reactivity was against peptide 1 (AA 22-41) with weaker reactivity against several other. peptides. The only exception was in mice immunized with ETSHR in TM which also showed significant reactivity against peptide 23 (AA 352-371). Mice immunized with the ETSHR in CFA or in TM showed elevated levels of serum TSH binding inhibitory immunoglobulins (TBII). However, mice immunized with ETSHR in Gerbu, which had lower titers of antibodies to ETSHR, showed normal TBII levels. These studies showed that adjuvant composition could influence the titer, subclass and fine specificity of antibodies to ETSHR which in turn could affect the development of TBII activity.  相似文献   
940.
A live oral recombinant Salmonella vaccine strain expressing pneumococcal surface protein A (PspA) was developed. The strain was attenuated with Deltacya Deltacrp mutations. Stable expression of PspA was achieved by the use of the balanced-lethal vector-host system, which employs an asd deletion in the host chromosome to impose an obligate requirement for diaminopimelic acid. The chromosomal Deltaasd mutation was complemented by a plasmid vector possessing the asd+ gene. A portion of the pspA gene from Streptococcus pneumoniae Rx1 was cloned onto a multicopy Asd+ vector. After oral immunization, the recombinant Salmonella-PspA vaccine strain colonized the Peyer's patches, spleens, and livers of BALB/cByJ and CBA/N mice and stimulated humoral and mucosal antibody responses. Oral immunization of outbred New Zealand White rabbits with the recombinant Salmonella strain induced significant anti-PspA immunoglobulin G titers in serum and vaginal secretions. Polyclonal sera from orally immunized mice detected PspA on the S. pneumoniae cell surface as revealed by immunofluorescence. Oral immunization of BALB/cJ mice with the PspA-producing Salmonella strain elicited antibody to PspA and resistance to challenge by the mouse-virulent human clinical isolate S. pneumoniae WU2. Immune sera from orally immunized mice conferred passive protection against otherwise lethal intraperitoneal or intravascular challenge with strain WU2.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号